Method of heat treating copper base alloy



silicon, nickel, chromium and cobalt. type are age hardenable and normally are solution Patented Jan. 8, 1963 3,072,508 METHOD OF HEAT TREATING COPPER BASE ALLOY John F. Klement and Quentin F. Ingerson, Milwaukee,

Wis, assignors to Ampco Metal, Inc., Milwaukee, Wis.,

a corporation of Wisconsin N Drawing. Filed Feb. 15, 1961, Ser. No. 89,354

3 Claims. (Cl. 148-160) This invention relates to a copper base alloy containing nickel and silicon and having. high hardness and improved electrical conductivity over the common copper-nickelsilicon alloys.

. In electrical applications it is often desirable to use alloys having a combination of high hardness and high electrical conductivity. Alloys of this type are generally copper base alloys having additions of metals such as Alloys of this quenched and. then aged to obtain the maximum physical properties. For example, the patent to Corson, 1,658,186, describes a copper base alloy hardened by the precipitation of silicides of chromium, nickel and cobalt. In the Corson patent the alloy is initially heated to a solution temperature in the range of 750 to 975 C. or 1382 to 1787 F., and subsequently quenched to hold the bulk of the silicide in solid solution. After quenching, the Corson alloy is aged. at a temperature in the range of 250 to 600 C. or 482 to 1112 F. to cause the silicide precipifate.

The present invention is directed to a copper base alloy having improved hardness and electrical conductivity over the prior alloys. In general, the copper base alloy contains additions of silicon, nickel and chromium and the alloy is heat treated by heating to a temperature in the range of 850 to 1025 F., and subsequently furnace cooled to a temperature in the range of 750 to 900 F. The alloy is held at a temperature inthis range for a period of time sufficient to obtain the optimum precipitation of nickel and chromium silicides. After this holding period, the alloy is quenched to room temperature to complete the heat treatment.

The alloy heat treated in accordance with this procedure has improved electrical conductivity over prior materials and has high hardness. Furthermore, the alloy is not hot short and will not crack at elevated tempera tures as used in electrical applications.

As no solution quench is employed in the heat treatment, the problem of warping is eliminated and the cast article can more readily hold a critical dimension because there is no scale formation during the draw or age and subsequent quench.

The alloy to be heat treated in accordance with the invention has the following composition in weight percent:

Nickel percent 0.752.0 Silicon do 0.251.0 Chromium do 0.25-1.25 Copper Balance A specific analysis of the alloy falling within the above range is as follows in Weight percent:

electrolytic or cathode type, and to deoxidize the copper completely so that a minimum amount of oxides are present in the melt. The nickel is usually introduced into the melt in the form of a 50-50 nickel-copper alloy and the silicon is employed in the form of a 10% silicon-copper master alloy, while the chromium-is used in the form of a 5% chromium-copper master alloy.

The sequence of melting for best results is to first charge the copper and the copper-nickel alloy. After melting down, lithium-copper is added for deoxidation of the melt and the silicon-copper master alloy is subsequently added for further deoxidation. The chromium-copper alloy is then added to the melt. This procedure is used so that a minimum of time elapses from the time the chromium is added to the time the alloy is poured. The chromium tends to oxidize more easily than does the silicon or nickel and consequently it is preferred to add the chromium in the last stage of the sequence.

, After the alloy has been compounded, it is brought to a pouring temperature in the range of 2150 to 2200 F. for average size castings. After casting, the cooling rate is normal with no water quench being used.

The heat treatment which is employed to bring about the improved hardness and electrical conductivity consists of initially heating the alloy to a temperature in the range of 850 to 1025 F., with a temperature of about 950 F. being preferred. The rate of heating to this temperature is not critical and the alloy is held at the temperature within this range for a period of time sutiicient to obtain a uniform distribution of temperature.

After obtaining the uniform distribution of temperature, the alloy is furnace cooled to a temperature in the range of 750 to 900 F., and preferably about 850 F. The cooling to this range should be slower than 500 F. per hour per one inch of section thickness.

After the alloy has been slowiy cooled to this temperature range, it is held at this temperature for a time sufii- 'cient to obtain the optimum precipitation of the nickel and chromium silicides. The object is to have a minimum amount of nickel and chromium silicides in solution for it is desirable to have copper alone in the matrix so as to improve the conductivity of the alloy.

The alioy is held at this aging temperature for a period of at least one hour and generally for about two hours per one inch of section thickness of the alloy.

After the aging at this temperature range, the alloy is preferably quenched in oil, water or any similar quenching media to room temperature. The quenching rate is generally faster than 1000 F. per 5 minutes per one inch of section thickness. While quenching from the aging temperature is preferred, the alloy can be air or furnace cooled, but with the use of air or furnace cooling, a portion of the precipitated silicides may migrate or go back In addition to the above metals, the normal impurities that are associated with copper, silicon and nickel can be tolerated up to an amount of 0.35% Without altering the characteristics of thev alloy. he elements which can be present as impurities are cobalt, beryllium, phosphorus,

lithium, iron, Zirconium and titanium.

The heat treatment as described above provides the alloy with an electrical conductivity in the range of 40 to 45% of pure copper, as compared with a conductivity of 30 to 35% achieved in similar alloys subjected to a solution quench and subsequent aging treatment. Furthermore, the alloy heat treated in accordance with the invention has a Rockwell B hardness in the range of 75 to 85, while alloys heat treated with the solution quench and aged generally have a hardness of about 70 Rockwell B.

The alloy of the present invention can be statically cast, centrifugally cast, extruded, forged and welded and can be fabricated into articles of various shapes and sizes, particularly for use in electrical applications.

The alloy can be welded by using Weld rods of similar composition with either a heliarc or consumable electrode process. The weld deposits are then treated in the manner described above with the drifting age treatment followed by the quench to obtain the improved physical properties.

As the heat treatment of the invention eliminates the solution quench, the problem of warping of the article is eliminated and similarly, scale formation is reduced which thereby results in the article maintaining critical dimensions. Furthermore, with the use of the heat treatment and alloy composition of the present invention, the alloy has no hot shortness and will not crack at elevated temperatures.

Various modes of carrying out the invention are contemplated as being within the scope of the following claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention.

We claim:

1. A method of heat treating a copper base alloy containing from 0.75 to 2.0% nickel, 0.25 to 1.0% silicon, 0.25 to 1.25% chromium and the balance copper, comprising the steps of heating the alloy to a temperature in the range of 850 to 1025 F., holding the alloy at said temperature to obtain an even distribution of heat, furnace cooling the alloy to a temperature in the range of 750 to 900 F., holding the alloy at said last named temperature range for a period of time sufficient to obtain an optimum precipitation of nickel silicide and chromium silicide, and subsequently cooling the alloy to room temperature.

2. A method of heat treating an age hardenable copper and an electrical conductivity of to of pure base alloy having small additions of silicon, nickel and chromium to obtain a hardness of to Rockwell B copper, comprising the steps of heating the alloy to a temperature in the range of 850 to 1025 F., holding the alloy at said temperature to obtain an even distribution of heat, furnace cooling the alloy to a temperature in the range of 750 to 900 F. at a rate slower than 500 F. per hour per one inch of section thickness, holding the alloy at a temperature in the last named range for a period of time sutficient to obtain an optimum precipitation of nickel silicide and chromium silicide, and subsequently cooling the alloy at a rate faster than 1000 F. per 5 minutes per one inch of section thickness.

3. A method of heat treating a copper base alloy containing from 0.75 to 2.0% nickel, 0.25 to 1.0% silicon, 0.25 to 1.25% chromium and the balance copper, comprising the steps of heating the alloy to a temperature of about 950 F., furnace cooling the alloy to a temperature of about 850 F., maintaining the alloy at said last named temperature for a period of time sufficient to obtain the maximum precipitation of nickel silicide and chromium silicide, and subsequently quenching the alloy.

References Cited in the file of this patent UNITED STATES PATENTS 1,658,186 Corson Feb. 7, 1928 FOREIGN PATENTS 497,166 Canada Oct. 27, 1953 UNITED STATES PATENT OFFlCE CERTIFICATE, OF CORRECTION Patent No 3,072,508 January 8, 1963 John F0 Klement et ale It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 4, beginning with "and an electrical" strike out all to and including "75 to 85 Rockwell B" in line 6, same column 4, and insert instead base alloy having small additions of silicon nickel and chromium to obtain a hardness of 75 to 85 Rockwell B and an electrical conductivity of 40% to 50% of pure Signed and sealed this 27th day of August 1963.

(SEAL) Attest:

ERNEST w. SWIDER DAVID LADD Attesting Officer Commissioner of Patents 

1. A METHOD OF HEAT TREATING A COPPER BASE ALLOY CONTAINING FROM 0.75 TO 2.0% NICKEL, 0.25 TO 1.0% SILICON, 0.25 TO 1.25% CHROMIUM AND THE BALANCE COPPER, COMPRISING THE STEPS OF HEATING THE ALLOY TO A TEMPERATURE IN THE RANGE OF 850 TO 1025*F., HOLDING THE ALLOY AT SAID TEMPERATURE TO OBTAIN AN EVEN DISTRIBUTION OF HEAT, FURNACE COOLING THE ALLOY TO A TEMPERATURE IN THE RANGE OF 750 TO 900*F., HOLDING THE ALLOY AT SAID LAST NAMED TEMPERATURE RANGE FOR A PERIOD OF TIME SUFFICIENT TO OBTAIN AN OPTIMUM PRECIPITATION OF NICKEL SILICIDE AND CHROMIUM SILICIDE, AND SUBSEQUENTLY COOLING THE ALLOY TO ROOM TEMPERATURE. 